I yet have tried the solution you mentioned before going here posting my problem, since I searched with internet when having this trouble. But this doesn't work, there is a conflict of distribution, I can't.

Last time I did it there was a conflict distribution error (with the 3.4.79+ Linaro/Lubuntu distrubution pre-installed within my pcDuino3 nano updated up to Linaro 12.11 version); and now, I have burnt a NAND image and Ubuntu kernel image with one of your procedures with SD card and USB flask disk:

So that you know exactly with what system version I run when having conflict. I only made a "sudo apt-get update" one time with this fresh installation and a geany installation to edit the file with "sudo apt-get install geany --yes" and I got too another conflict distribution with the modification you indicated, but different this time, I have an indication of conflict ID key (I had not this conflict ID number with the same modification of sources with the preinstalled kernel inside the pcduino, I only had a conflict version error with nothing else):

Why? Because all upgrade was successfull and everything works great, until I install gdebi package (to install package graphically). Then my X windows sessions was a black screen. I tried many things and understood that LXDE was running but not displaying anything (I could use Ctrl+Alt+F1 to see it) and this is because gdebi package from trusty source is NOT compatible with the pcduino kernel provided (although upgraded to 14.04.5LTS), changes some X server configuration and ... X server gives a black screen. But gdebi is not the only one. I installed too pavucontrol after going on 14.04 and then... the same black screen. We obtain black screen with some updates of packages concernong X windows and then pcduino won't work any longer. Stay with 12.04.

So DON'T USE trusty first (you can install gdebi first with precise sources, pavucontrol, in Lubuntu 12.04 and then upgrade to trusty after, then no black screen occurs, but don't install anything else afeter going on 14.04 unless you have the risk of black screen). I burnt many times NAND and kernel and reinstalled everything and testes many things and that is my conclusion.

I had the ID keys mismatch only with trusty sources (Lubuntu 14.04), no problem with precise sources (Lubuntu 12.04)

2)Second thing: I found the problem, why there is a distribution conflict when using the lines added to sources.list:

The first part: "http://ubuntu.pcduino.com/pcduino3/"is the base url, then you have a space between this base url and pcduino, it means that you must have a subdir named "dists", then you have another space between pcduino and main, thos means that you access the subdir and file "main/source/Sources". This is the way source packages are meant to be built.

The file "Sources" lists all the files in the subdir "source" and their size and checksum.

We can see that the kernel files for pcduino3 is here: "pcduino-kernel_0.1_armhf.deb " and the headers sources for compiling kernel 3.4.79+ to compile your drivers is here too "pcduino-linux-headers-3.4.79+_0.1_armhf.deb".

So all is here. But we can't access it because it is at the wrong place.

So, if an admin here could replace the files at the correct place the firts post of this topic would be a suefull instruction since the apt-get sources would be right.

I can say that those files are the right ones, since I downloaded the headers for 3.4.79+ and could use them. So if no admin action is taken to repair the wrong file place, you can do it like me:

Use your Chromium web browser in Lubuntu 12 of your pcduino to download the package you want (for me the headers of the kernel):

(or use a wget command line instruction if you wish), and then install the package you just downloaded (I installed it in graphic mode with gdedi and double click on the .deb file) and then ... it works!

If you just want to laucnh command lines to do it with no search of what to do, I put here the instructions: